THE HISTORY OF A DISCOVERY. 47 



the forms in the beds, and their association with layers 

 of fragmental Eozoon, are strictly in accordance with 

 the theory that these old Laurentian limestones are 

 truly marine deposits, holding the remains of the sea 

 animals of their time. 

 ^k, Eozoon is not, however, the only witness to the 

 great fact of Laurentian life, of which it is the most 

 conspicuous exponent. In many of the Laurentian 

 limestones, mixed with innumerable fragments of 

 Eozoon, there are other fragments with traces of 

 organic structure of a different character. There are 

 also casts in silicious matter which seem to indicate 

 smaller species of Foraminifera. There are besides 

 to be summoned in evidence the enormous accumula- 

 tions of carbon already referred to as existing in the 

 Laurentian rocks, and the worm-burrows, of which 

 very perfect traces exist in rocks probably of Upper 

 Eozoic age. 



Other discoveries also are foreshadowed here. The 

 microscope may yet detect the true nature and affi- 

 nities of some of the fragments associated with Eozoon. 

 Less altered portions of the Laurentian rocks may be 

 found, where even the vegetable matter may retain its 

 organic forms, and where fossils may be recognised by 

 their external outlines as well as by their internal 

 structure. The Upper Laurentian and the Huronian 

 have yet to yield up their stores of life. Thus the 

 time may come when the rocks now called Primordial 

 shall not be held to be so in any strict sense, and when 

 swarming dynasties of Protozoa and other low forms 



